Visible-Light Driven Photoelectrochemical Platform Based on the Cyclometalated Iridium(III) Complex with Coumarin 6 for Detection of MicroRNA

Abstract

In this study, a novel iridium(III) complexbased photoactive species, [(C6) 2 Ir(dppz)] + PF 6 − , was synthesized with coumarin 6 (C6) as a cyclometalated ligand and dipyrido[3,2-a:2′,3′-c]phenazine (dppz) as an ancillary ligand. The photophysical and electrochemical properties of the complex have been investigated. It exhibits intense visiblelight absorption with a molar extinction coefficient up to 9.8 × 10 4 M −1 cm −1 at 485 nm. The photoelectrochemical (PEC) properties of [(C6) 2 Ir(dppz)] + PF 6 − were also investigated by spin-coating on the ITO electrode. By illumination with 490 nm light, cathodic photocurrent up to 260 nA/cm 2 was observed at 0 V bias potential with dissolved O 2 as an electron acceptor. On the other hand, an anodic photocurrent was generated in the presence of triethanolamine (TEOA) as a sacrificial electron donor. The probable mechanisms for photocurrent generation were deduced by UV−vis absorption spectrum and cyclic voltammetry data. Adopting [(C6) 2 Ir(dppz)] + PF 6 − as photoactive intercalator, a visible-light driven PEC detection platform was successfully fabricated for microRNA detection based on an enzyme-free hybridization chain reaction as an amplification strategy. Expected, the PEC platform for microRNA-122b detection showed excellent linear response with a limit of detection down to 0.23 fM (3σ), comparable or superior to those of the reported analogous approaches. Encouragingly, this study would provide a new approach to exploit efficient photoactive species for PEC bioanalysis.

A Roadmap Towards Visible Light Mediated Electron Transfer Chemistry with Iridium(III) Complexes

“…IrC 2 N 4 (Figure 11) complexes probably represent the best studied class of iridium complexes due to the very wide range of accessible ground‐ and excited‐state redox potentials. They have indeed been used for several applications that include, amongst others, CO 2 and H + reduction, [34b,36a,64] halide oxidation, [8] dye‐sensitized solar cells [65] and biosensing [66] …”

“…Cyclometalation of coumarin (C6) was also reported to drastically increase the visible light absorption properties of iridium complexes, with molar absorption coefficients around 480 nm that span 40000–150000 M −1 cm −1 ( Ir50 – 55 ). This allowed the development of iridium (III) complexes with uses in hydrogen photoproduction, [68–69] DSSCs, [65] upconversion [46a,70] or as biosensors, [66,71] for example. Ir50 was reported as a sensitizer for both n ‐type and p ‐type DSSCs.…”

<p>MicroRNA-195 as a prognostic factor for cancer survival outcome in China: a meta-analysis</p>

“…Cancer-associated miRNAs act by binding to the 3ʹ-untranslation region (UTR) of specific mRNAs and play a significant and multifaceted role in the development and progression of tumors 31. A large number of miRNAs have been found to be associated with clinical features of a variety of cancers.…”

Avenues Toward microRNA Detection In Vitro: A Review of Technical Advances and Challenges

“…Photoelectrochemical (PEC) sensing, as a vibrant electrochemical analytical technology, exhibits striking advantages such as instinctive mechanism and prominent anti-interference for chemical analysis [109]. Notably, PEC analysis involves the conversion of photoactive materials from photo to electricity in which the photo-induced formation of electron-hole pairs in a photoactive material is utilized to initiate oxidation–reduction reactions [110,111]. Therefore, for PEC biosensors, eminent photoactive materials with appropriate band gap, high carrier mobilities, good corrosion resistance, and relatively low cost are critical to performance [109].…”

“…Therefore, for PEC biosensors, eminent photoactive materials with appropriate band gap, high carrier mobilities, good corrosion resistance, and relatively low cost are critical to performance [109]. Based on that, several novel species with distinctive properties were constructed and applied in PEC biosensor as photoactive materials, such as a MoS 2 /g-C 3 N 4 /black TiO 2 heterojunction [112], a novel iridium(III)-complex-based photoactive material [111], and a TiO 2 -α-Fe 2 O 3 heterojunction [109], to greatly improve the PEC performance of electrode.…”